Another alternative is a LiFePo4 cell. These have a nominal voltage of 3.3v
as opposed to LiPO Batteries which have a nominal voltage of 3.7v. They are
also ultra cheap off of ebay and are far less volatile than LiPO, designed
to be bullet proof for battery powered tools and hybrid cars.
http://shop.ebay.com/?_from=R40&_trksid=p5197.m570.l1313&_nkw=a123+18650&_sacat=See-All-Categories
These are safe to recharge with an off the shelf wall wart between 3.3v and
3.6v.
On Tue, Jan 4, 2011 at 2:07 PM, Jonathan Foote <jtfoote at ieee.org> wrote:
> A likely problem is the dropping resistors which waste power. Also 9V
> batteries are not great for power density.
>> Several solutions: as was mentioned, a coin cell battery will happily
> drive one or two LEDs for a good long time.
>> Another approach is to use a "Joule Thief" circuit and a single AA. JFGI.
>> In the overengineering department, a LiPo battery (of which there are
> boxes full at NB) plus a constant current SEPIC driver would be most
> efficient, and rechargeable to boot.
>> Or just use the LiPo with dropping resistors; SparkFun sells a
> charging circuit chip + breakout board so you can recharge it from a
> USB port. No wasted batteries!
>>> -J
>>> On Tue, Jan 4, 2011 at 12:06 PM, meredith scheff <satiredun at gmail.com>
> wrote:
> > I'd like to do a soft circuit scarf or three, but I'm always running up
> > against the problem of power. I usually use fairly low power LEDs
> > (<2v) driven by a 9v battery or one of sparkfun's LiPos.
> > I've heard tell of somehow being able to power more, but I'm still
> learning
> > this EE stuff. Could some kind person point me in the right direction?
> > Meredith
> >
> > --
> >
> > Ladycartoonist.com
> >
> > ___________
> >
> > A human being should be able to change a diaper, plan an invasion,
> butcher a
> > hog, conn a ship, design a building, write a sonnet, balance accounts,
> build
> > a wall, set a bone, comfort the dying, take orders, give orders,
> cooperate,
> > act alone, solve equations, analyze a new problem, pitch manure, program
> a
> > computer, cook a tasty meal, fight efficiently, die gallantly.
> > Specialization is for insects.
> >
> > -Robert A. Heinlein
> >
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